Image display apparatus for fixing luminance of blank area and varying only luminance of image

ABSTRACT

An image display apparatus fixes the luminance of a blank area and varies only the luminance of an image. The image display apparatus includes an A/D conversion device to convert an input analog image signal into digital image data, a black level setting device for setting the black level of the digital image data by adjusting a lower-limit reference voltage of the A/D conversion device, a blank data generation device to generate blank data to display a blank area around an image display area on the screen, an image data combining device to combine the blank data generated by this blank data generation device and the digital image data output from the A/D conversion device, and a display device to display the output of this image data combining device on the screen.

This application claims the benefit of priority to Japanese PatentApplication 11-190996, filed on Jul. 5, 1999.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an image display apparatus.

2. Description of the Related Art

Generally, image display apparatuses include a function for adjustingthe black level, that is, the level at which the luminance is lowest inan image to be displayed on a monitor of these apparatuses.Conventionally, in order to realize this function, a method is used tovary a γ correction voltage in a γ correction circuit. This γ correctioncorrects the characteristics of gradation (degree of luminancevariation) of an image to linear characteristics, and use of thiscorrection also makes it possible to adjust the black level at which theluminance is lowest.

Meanwhile, there is a case in which a blank area is displayed on animage display apparatus such as that described above so that a blankingmark indicating a photographic range of a video camera, etc., isdisplayed superimposed on an image. This blank area is often displayedat the black level at which the luminance is lowest. It is preferablethat the black level of this blank area always be at a predeterminedlevel without being influenced by the luminance of an image to bedisplayed.

However, if attempts to vary the black level by a method which uses theabove-described γ correction circuit are made, since this γ correctioncircuit is provided immediately before a driver which drives a displaymechanism, such as an LCD, and a combined image after the blank area andthe image are combined together is corrected, there is a problem in thatthe luminances of both of the blank area and the image vary at the sametime.

SUMMARY OF THE INVENTION

The present invention has been achieved to solve the above-describedproblem. An object of the present invention is to provide an imagedisplay apparatus capable of fixing the luminance of a blank area andvarying only the luminance of an image.

To achieve the above-mentioned object, according to the presentinvention, there is provided an image display apparatus comprising anA/D converter to convert an input analog image signal into digital imagedata; a black level setting mechanism to set the black level of thedigital image data by adjusting a lower-limit reference voltage of theA/D converter; a blank data generator to generate blank data to displaya blank area around an image display area on a screen; an image datacombiner to combine blank data generated by this blank data generatorand digital image data output from the A/D converter; and a display todisplay an output of this image data combiner on the screen.

According to the image display apparatus of the present invention, theblack level of an image display area can be adjusted by a black levelsetting mechanism independently of the data of the blank area.

Preferably, the black level setting mechanism is a variable resistor.The black level setting mechanism preferably includes an illuminancesensor to detect the illuminance of the surroundings of a video camera,which outputs an analog image signal so that the black level isautomatically set in correspondence with the illuminance of thesurroundings of the camera.

The automatic setting of the black level is complete since theilluminance sensor outputs a lower-limit reference voltage correspondingto the detected illuminance.

The above and further objects, aspects and novel features of theinvention will become more fully apparent from the following detaileddescription when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an image display apparatus according toa first embodiment of the present invention;

FIG. 2 is a diagram of circuits peripheral to an A/D converter;

FIG. 3 is a diagram showing the relationship between an image display ofan LCD and a combined image signal;

FIG. 4 is a timing chart of a video signal; and

FIG. 5 is a schematic diagram of an image display apparatus according toa second embodiment of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The construction of an image display apparatus 1, which is aprogrammable logic device (PLD), according to a first embodiment of thepresent invention is described below with reference to FIG. 1. The imagedisplay apparatus 1 is provided with input terminals 1 a, 1 b, and 1 cfor inputting a video signal from the outside. Also, the image displayapparatus 1 has contained therein a Y/C separation RGB decoding circuit2, an A/D converter 3, a variable resistor 6, an image signal processingcircuit 7, a gate driver 13, a source driver 14, a γ correction circuit15, a 6-inch high-resolution TFT LCD 16 having 962×562 pixels, abacklight 17, and an inverter 18.

The input terminal 1 a is connected to the input terminal of the Y/Cseparation RGB decoding circuit 2, and the output terminal of the Y/Cseparation RGB decoding circuit 2 is connected to the input terminal ofthe A/D converter 3. The input terminals 1 b and 1 c are connecteddirectly to the input terminal of the A/D converter 3.

The variable resistor 6 has three terminals, a second terminal thereofextending from the middle of the resistor so as to allow variation ofthe connection point with the resistor. The first and third terminalsextend from both ends of the resistor. Therefore, the resistance valuebetween the first terminal and the second terminal, and the resistancevalue between the second and the third terminal are variable. The secondterminal is connected to the input terminal of the A/D converter 3. Thefirst terminal is fixed to an upper-limit reference voltage Vh, and thethird terminal is connected to a ground potential.

The output terminal of the A/D converter 3 is connected to the inputterminal of the image signal processing circuit 7. The output of thisimage signal processing circuit 7 is connected to the input terminals ofthe gate driver 13 and the source driver 14. The output terminal of theγ correction circuit 15 is connected to the input terminal of the sourcedriver 14.

The output terminals of the gate driver 13 and the source driver 14 areconnected to the input terminal of the LCD 16 so that each pixel of theLCD 16 is driven. The output terminal of the inverter 18 is connected tothe input terminal of the backlight 17, and the inverter 18 drives thebacklight 17. The backlight 17, disposed in the back of the LCD 16,emits transmission light which passes through this LCD 16 from the backof the LCD 16 so that this transmission light illuminates the LCD 16.

Referring also to FIG. 1, the internal construction of the A/D converter3 is described below. The A/D converter 3 has contained therein aclamping circuit 4 and an A/D conversion circuit 5. The three inputterminals provided in the A/D converter 3 are connected to the inputterminal of the clamping circuit 4, and the output terminal of thisclamping circuit 4 is connected to the input terminal of the A/Dconversion circuit 5. The output terminal of the A/D conversion circuit5 is connected to the output terminal of the A/D converter 3. The inputterminal of the A/D converter 3, which is connected to the secondterminal of the variable resistor 6, is connected to the input terminalof the lower-limit reference voltage of the A/D conversion circuit 5.

Referring also to FIG. 1, the internal construction of the image signalprocessing circuit 7 is described below. The image signal processingcircuit 7 has contained therein an image data conversion circuit 8, ablank data generation circuit 9, a blanking marker generation circuit10, an image data combining circuit 11, and an LCD controller 12.

The input terminal of the image signal processing circuit 7 is connectedto the input terminal of the image data conversion circuit 8. The outputterminals of the image data conversion circuit 8, the blank datageneration circuit 9, and the blanking marker generation circuit 10 areconnected to the input terminal of the image data combining circuit 11.The output terminal of the image data combining circuit 11 is connectedto the input terminal of the LCD controller 12, and the output terminalof this LCD controller 12 is connected to the output terminal of theimage signal processing circuit 7.

Next, referring to FIG. 2, a detailed circuit construction of theperiphery of the A/D converter 3 is described. A video signal from theinput terminal of the image display apparatus 1 or from the outputterminal of the Y/C separation RGB decoding circuit 2 is input to aterminal Vin of the A/D converter 3 through a capacitor 19. A clocksignal is input to a terminal CLK of the A/D converter 3. A clampingpulse is input to a terminal CLP of the A/D converter 3. A clampingvoltage is input to a terminal Vref of the A/D converter 3.

A lower-limit reference voltage output from the second terminal of thevariable resistor 6, which is connected to a reference voltage source 20output from the second terminal of the variable resistor 6, is input tothe terminal Vl of the A/D converter 3. An upper-limit referencevoltage, which is output from the reference voltage source 20 through avariable resistor 21, is input to a terminal Vh of the A/D converter 3.The output terminal on the negative side of the reference voltage source20 is connected to a ground potential. An 8-bit digital signal is outputfrom the output terminals D0 to D7 of the A/D converter 3. This digitalsignal takes a digital value such that the section between thelower-limit reference voltage and the upper-limit reference voltage isdivided evenly by 256, that is, an 8-bit digital value.

Next, referring to FIG. 1, the operation of this embodiment isdescribed. A video signal, which is an analog signal, is input from theinput terminals 1 a, 1 b, or 1 c provided in the image display apparatus1. In a case where a video signal is input from the input terminal 1 a,this video signal is input to the A/D converter 3 after passing throughthe Y/C separation RGB decoding circuit 2. In a case where a videosignal is input from the input terminal 1 b or 1 c, the input videosignal is input directly to the A/D converter 3.

The black level, that is, the level at which luminance is lowest, of thevideo signal which is input to the A/D converter 3 is clamped by theclamping circuit 4 contained in the A/D converter 3. The A/D conversioncircuit 5 digitizes the video signal, whose black level is clamped. Thedigitized video signal is output from the A/D converter 3 and is inputto the image signal processing circuit 7.

The digitized video signal, which is input to the image signalprocessing circuit 7, is converted into image data by the image dataconversion circuit 8 contained in the image signal processing circuit 7,and is input to the image data combining circuit 11. Blank data outputfrom the blank data generation circuit 9 contained also in the imagesignal processing circuit 7 is also input to the image data combiningcircuit 11. This blank data contains a signal that specifies a blacklevel in a blank area on the screen.

Furthermore, a blanking marker signal output from the blanking markergeneration circuit 10 is also input to the image data combining circuit11. This blanking marker signal contains a signal that specifies a whitelevel (level at which the luminance is highest) of a boundary linebetween the image display area of the screen and the blank area thereof.The image data combining circuit 11 combines the image data, the blankdata, and the blanking marker signal, and outputs the combined imagedata to the LCD controller 12.

The LCD controller 12 converts the combined image data into an LCDdriving signal and outputs the converted LCD driving signal to the gatedriver 13 and the source driver 14. The LCD 16 is driven by the gatedriver 13 and the source driver 14, and a combined image formed by thecombined image data is displayed on the LCD 16.

The γ correction circuit 15 sends a γ correction voltage to the sourcedriver 14 so that γ correction of the image is performed. Also, theinverter 18 drives the backlight 17 so that this backlight 17 suppliestransmission illumination light from the back of the LCD 16.

Next, referring to FIG. 3, the relationship between combined imagedisplayed on the screen of the LCD 16 and a combined image data (videosignal) is described. A screen 16 a of the LCD 16, shown at (b) in FIG.3, is divided into an image display area 16 b and a blank area 16 c. Inthe image display area 16 b, an image formed by the video signal inputto the image display apparatus 1, that is, an image within thephotographic range of a video camera or the like, is displayed. In theblank area 16 c, a black level determined in accordance with blank datagenerated by the blank data generation circuit 9 is displayed.

A waveform of combined image data (video signal) to display a particularline 16 d in the horizontal direction on the screen 16 a is shown at (a)in FIG. 3. In this embodiment, one line in the horizontal direction iscomposed of 960 pixels, and among them, the number of pixels of theimage display area 16 b is 647. The blank area 16 c is equally providedon the right and left of the image display area 16 b. The line 16 d isscanned from left to right. The blank area 16 c is also equally providedin the upper and lower portions of the image display area 16 b.

A first interval A of the line 16 d is drawn by an interval A′ of avideo signal, an interval B is drawn by an interval B′, and an intervalC is drawn by an interval C′. The signal level of the interval A′ andthe interval C′ is a black level determined in accordance with the blankdata generated by the blank data generation circuit 9.

Also, a blanking marker signal is inserted between the interval A′ andthe interval B′ and between the interval B′ and the interval C′. Theseblanking marker signals correspond to one pixel between the interval Aand the interval B and between the interval B and the interval C in theline 16 d on the screen 16 a. Therefore, as a result of scanning by theline 16 d being repeated, a white line is displayed vertically betweenthe interval A and the interval B and between the interval B and theinterval C on the screen 16 a.

The blank areas displayed in the upper and lower portions of the screen16 a are displayed by the line at this position by drawing the blacklevel of the blank area over one horizontal period.

The black level of the blank area 16 c differs from the black level ofthe image display area 16 b, each of which is determined by a mutuallydifferent signal. That is, the black level of the blank area 16 c isdetermined by the blank data generated by the blank data generationcircuit 9, and the black level of the image display area 16 b isdetermined by the lower-limit reference voltage input to the terminal V1of the A/D converter 3. The variable resistor 6 adjusts the lower-limitreference voltage.

Since the blank data generated by the blank data generation circuit 9does not pass through the A/D converter 3, even if the lower-limitreference voltage is changed, this blank data is not affected by thischange. Therefore, even if the lower-limit reference voltage is adjustedby the variable resistor 6 and the black level of the image display area16 b is adjusted, the black level of the blank area 16 c does notchange.

Next, referring to FIG. 4, a sampling operation of a video signal isdescribed. The black level (the level at which the luminance is lowest)of the input video signal is determined by the clamping voltage, whichhas been input to the terminal Vref when a clamping pulse is input tothe CLP terminal of the A/D converter 3. The digital signal output fromthe A/D converter 3 becomes a value determined by the relationshipbetween the clamping voltage and the lower-limit reference voltage inputto the terminal Vl of the A/D converter 3. The sampling of the videosignal is performed in synchronization with the clock signal input tothe terminal CLK of the A/D converter 3.

Next, referring to FIG. 5, a second embodiment of the present inventionis described. The same components in FIG. 5 as those of the firstembodiment are given the same reference numerals, and accordingly,descriptions thereof are omitted. In the second embodiment, instead ofthe variable resistor 6 in the first embodiment, an illuminance sensor23 and a lower-limit reference voltage generation circuit 22 areprovided. The illuminance sensor 23 is disposed, for example, near avideo camera or the like which outputs a video signal to be input to theimage display apparatus 1, and measures the illuminance near this videocamera or the like. The output of the illuminance sensor 23 is input tothe lower-limit reference voltage generation circuit 22, whereby alower-limit reference voltage corresponding to this input is output fromthe lower-limit reference voltage generation circuit 22, and this outputis input to the A/D conversion circuit 5 inside the A/D converter 3.

With such a construction, the lower-limit reference voltageautomatically changes in accordance with the illuminance around thevideo camera or the like. Therefore, if the surroundings of the videocamera or the like are bright, the lower-limit reference voltage alsoincreases, and the black level of the signal also increases inaccordance with this voltage. If, in contrast, the surroundings of thevideo camera are dark, the lower-limit reference voltage decreases, andthe black level of the signal also decreases in accordance with thisvoltage. However, since the black level of the blank area is determinedonly by the blank data output from the blank data generation circuit 9,and this blank data does not pass through the A/D conversion circuit 5to which the lower-limit reference voltage is applied, even if theilluminance of the surroundings of the video camera or the like changes,this change is detected by the illuminance sensor 23, and thelower-limit reference voltage is changed as a result of this detection,the black level of the blank area does not change.

According to the present invention, since the black levels of an imagedisplay area and a blank area can be set individually, even if theluminance of an image to be displayed is changed by adjusting the blacklevel of the image display area, the black level of the blank area doesnot change.

Many different embodiments of the present invention may be constructedwithout departing from the spirit and scope of the present invention. Itshould be understood that the present invention is not limited to thespecific embodiments described in this specification. To the contrary,the present invention is intended to cover various modifications andequivalent arrangements included within the spirit and scope of theinvention as hereafter claimed. The scope of the following claims is tobe accorded the broadest interpretation so as to encompass all suchmodifications, equivalent structures and functions.

1. An image display apparatus comprising: a screen capable of displayingan image area and a blank area; an A/D converter to convert an inputanalog image signal into digital image data; a black level settingmechanism to set a first black level of the digital image data byadjusting a lower-limit reference voltage of the A/D converter; a blankdata generator to generate blank data to form the blank area around theimage display area, a second black level of the blank area beingindependent of the first black level of the digital image area; an imagedata combiner to combine the blank data and the digital image data; andan output of the image data combiner being displayed on said screen. 2.An image display apparatus according to claim 1, said black levelsetting mechanism comprising a variable resistor.
 3. An image displayapparatus according to claim 1, said black level setting mechanismcomprising an illuminance sensor to detect the illuminance around avideo camera that outputs said analog image signal.
 4. An image displayapparatus according to claim 3, wherein said black level settingmechanism outputs a lower-limit reference voltage corresponding toilluminance detected by said illuminance sensor.
 5. The image displayapparatus according to claim 1, further comprising a blanking markersignal corresponding to a single pixel between the blank area and theimage display area such that a white line is vertically displayed on thescreen which separates the blank area and the image display area.
 6. Amethod of displaying an image comprising: converting an input analogimage signal into digital image data; adjusting a lower-limit referencevoltage of the digital image data to thereby adjust a first black levelof the digital image data; generating blank data for display in a blankarea around an image display area in which a second black level of theblank data is independent of the first black level of the digital imagedata; combining the blank data and the digital image data; anddisplaying the digital image data in the image display area and theblank data in the blank area of a display screen.
 7. The method ofdisplaying an image according to claim 6, the adjusting the first blacklevel comprising adjusting a variable resistor.
 8. The method ofdisplaying an image according to claim 6, the adjusting the first blacklevel comprising detecting an illuminance around a video camera thatoutputs the analog image signal.
 9. The method of displaying an imageaccording to claim 8, further comprising outputting a lower-limitreference voltage corresponding to the detected illuminance.
 10. Themethod according to claim 6, further comprising separating the blankarea and the image display area on the screen by a white line of asingle pixel corresponding to a blanking marker signal.
 11. A method ofdisplaying an image comprising: converting an input analog image signalinto digital image data; adjusting a lower-limit reference voltage ofthe digital image data to thereby set a first black level of the digitalimage data; generating blank data for display in a blank area around animage display area in which a second black level of the blank data isindependent of the first black level of the image display data;combining the blank data and the digital image data; and displaying thecombination of the blank data and the digital image data on a screen.12. The method according to claim 11, the setting of the first blacklevel comprising adjusting a variable resistor.
 13. The method accordingto claim 11, the setting of the first black level comprising detectingan illuminance around a video camera that outputs the analog imagesignal.
 14. The method according to claim 13, further comprisingoutputting a lower-limit reference voltage corresponding to the detectedilluminance.
 15. The method according to claim 11, further comprisingfurther comprising separating the blank area and the image display areaon the screen by a white line of a single pixel corresponding to ablanking marker signal.